Molecular properties of various snail peptides from brain and gut.

Attention is focused on the similarities in primary structure of the egg-laying neurohormone of the pulmonate Lymnaea stagnalis and of the opisthobranch Aplysia californica which both consist of 36 amino acid residues. FMRFamide-like peptides have now been isolated and sequenced from six molluscan species. Besides FMRFamide, two closely related peptides were isolated from the central nervous system of L. stagnalis and sequenced. This indicates that a family of FMRFamide-like peptides exist not only in the molluscs, but also within one species. A molluscan growth hormone, isolated from the brain of L. stagnalis, has been characterized. This small peptide hormone stimulates in vitro a receptor-adenylate cyclase system of mantle edge cells and in vivo the Ca2+-incorporation in the shell edge. The biochemical characterization of three vertebrate-like peptides of L. stagnalis, resembling oxytocin, Arg-vasopressin, and insulin, confirms the immunological findings that gastropods contain peptides which are structurally closely related to mammalian peptides.